Orthopedic surgeons currently use X-rays to assess how patients with fractured limbs or ligament tears are progressing toward healing. X-rays unfortunately provide an incomplete picture for the surgeon. An X-ray will only provide an instantaneous picture of the fractured limb, for example. It will not provide the surgeon with information related to the amount of stress the patient has been placing on the fractured limb during the healing process. This additional information, if available, could assist the surgeon with their treatment decisions. For example, if a surgeon knows that a patient is putting too much load on the limb for a given fracture type, the surgeon could advise the patient to “take it easy” on the limb. Similarly, if the patient is not placing enough load on the limb, the surgeon can advise the patient as to the need for physical activity and/or physical therapy.
Moreover, if the patient has a surgical implant, an X-ray will not provide the surgeon with an indication of the amount of load that the patient has been putting on the implant. A surgeon armed with this information could evaluate the risk of implant failure and modify their treatment decisions accordingly.
Devices have previously been developed that attempt to provide a surgeon with more information regarding a patient's healing progress. For example, U.S. Pat. No. 6,034,296, issued Mar. 7, 2000 to Niell Elvin et al., is directed to an implantable bone strain telemetry sensing system and method. The system includes a strain sensor affixed to a bone fixing device. The sensor measures the strain in the bone fixing device by generating a strain signal in response to stress applied to the device. The strain sensor provides the strain data to an external receiver via wireless communications. The purpose of the system is to provide an indication of the extent of healing of a bone. The strain sensor is placed in a location such that it can measure strain on the fixation device. The patient is subjected to a series of exercises, and the strain on the fixation device is measured. It is expected that for a given stress level the strain on the fixation device will be reduced as the bone heals, as the bone will be able to absorb more of the stress.
The Elvin device is limited in the information it can provide to the surgeon. For example, as the bone heals, the device will provide less and less information to the surgeon—as discussed above, the strain sensor only registers data when the fixation device is stressed, and the amount of strain on the device will decrease as the bone heals. A sudden or unexpected increase in measured strain could indicate possible device failure or inadequate bone healing, but it will not provide an indication of the types or amount of stress that the patient has been applying to the implant, or whether the patient is following the surgeon's healing instructions. Nor does it provide an indication of whether the patient is putting enough or too much load on the injured limb. Moreover, one of the important features of the Elvin device is that it generates its own power by utilizing a piezoelectric-based material. These piezoelectric-based materials are complex and relatively costly.
Accordingly, there is a need for an improved device to address these shortcomings and provide surgeons with additional information to improve the healing assessment and assist with their treatment decisions.